Dry,cardable,self-bondable fibers of regenerated cyanoethyl cellulose

ABSTRACT

Dry, soft, cardable, self-bondable fibers of regenerated cyanoethyl cellulose having an average degree of substitution of from about 0.25 to about 0.65 which have been prepared by neutralizing wet-gel fibers of regenerated cyanoethyl cellulose while maintaining them in a substantially non-swollen condition in a concentrated aqueous salt solution, contacting the fibers with a lubricant for cellulosic fibers under non-swelling conditions, and then drying the fiber down to at least a normal moisture regain content.

United States Patent Matter et a1.

DRY, (IARDABLE, SELF-BONDABLE FIBERS OF REGENERATED CYANOETHYL CELLULOSE lnventors: Theodore S. Matter, Upper Darby;

James E. McMaster, Secane, both of Pa.

Alssignee: FMC Corporation, Philadelphia, Pa.

Filed: Jan. 8, 1971 Appl. No.: 105,101

us. c1 ..117/139.s CQ, 117/126 R,"

CF, 117/140 R, 117/141, 117/143 R, 117/144, 23/1375 1m. 01. ..D06m 13/40 Field ofSearch ..117/13s.s UA, 139.5 CF,

139.5 CQ, 117/140 11,144,166, 126 R, 141,143 R; 260/232; 106/164 l 1March 20, 1973 References Cited UN lTED STATES PATENTS 3,419,345 12/1968 Parrish ..106/l64 X 3,525,735 8/1970 Miller. ..260/231 2,668,785 2/1954 Jefferson et a1. ..117/139.5

Primary Examiner-William D. Martin Assistant Examiner-Theodore G. Davis Attorney-Thomas R. OMalley, George .F. Mueller and Robert G. Hoffmann [57] ABSTRACT 10 Claims, No Drawings DRY, CARDABLE, SELF -BON DABLE FIBERS OF REGENERATED CYANOETHYL CELLULOSE Regenerated cyanoethyl cellulose fibers have heretofore been disclosed as bonding agents in non-woven fabrics. Because of the difficulty in obtaining commercially acceptable dry, soft, cardable regenerated cyanoethyl cellulose fibers which have bonding properties in non-Wovens employing as little as 2 percent of these fibers, their use has been restricted to wet systems for the preparation of non-woven webs. US. Pat. No. 3,525,735 to l. K. Miller discloses that dry, cardable regenerated cyanoethyl cellulose yarn may be obtained by either replacement of water by acetone and evaporation of the acetone or by applying a finish or wetting agent to the acidic wet-gel yarn and drying the swollen yarn with heat. The former method is objectionable since the solvent recovery is too expensive. The latter method is objectionable since the dry product is boardy and not supple enough for use in the manufacture of commercially suitable non-Wovens in the so-called dry forming method. In any event, it is recognized that, for manufacturing convenience, it would be more practical to be able to dry the unswollen never-dried (gel) regenerated cyanoethyl cellulose fibers which have been neutralized and maintained in an unswollen condition by treatment with an aqueous buffered salt solution as disclosed, for example, in US. Pat. No. 3,419,345 to E. G. Parrish. Using a salt dewatering procedure, the swellable cyanoethylated cellulose yarn may be brought to a water content of as low as about percent by careful pressing of centrifuging, but this is merely an added step and it does not produce a dry product which contains waterin an amount equivalent to about normal moisture regain.

It is an object of this invention to provide dry, soft, cardable, self-bondable fibers of regenerated cyanoethyl cellulose wherein the average degree of substitution of the cellulose is from about 0.25 to about 0.65.

It is another object of this invention to provide nonwoven fabrics utilizing dry, soft, cardable, self-bondable fibers of regenerated cyanoethyl cellulose wherein said fibers provide durable non-Wovens of good strength.

These and other objects are accomplished in accordance with this invention which comprises dry, cardable, self-bendable fibers or regenerated cyanoethyl cellulose wherein the average degree of substitution ranges from about 0.25 to about 0.65, preferably about 0.35 to 0.45, said dry fibers having been prepared by neutralizing unswollen acidic gel fibers of regenerated cyanoethyl cellulose with an aqueous concentrated buffered salt solution and bringing the wet fibers in intimate contact with a lubricant for cellulosic fibers under non-swelling conditions, and

then drying the fibers to a water content which will permit the fibers to be carded.

This invention also pertains to non-Wovens comprising at least about 2 percent by weight of the above regenerated cyanoethyl cellulose fibers as a bonding agent.

The term regenerated cyanoethyl cellulose" as used herein refers to a regenerated product obtained either from viscose to which acrylonitrile is added or viscose prepared by the simultaneous cyanoethylation and xanthation of alkali cellulose. The latter preparation is preferred based on better economics and is described by A. l. Bates in US. Pat. No. 3,146,116 of Aug. 25, 1964, as well as US. Pat. No. 3,525,735, supra. Regeneration of the viscose is accomplished by means of a conventional acidic type coagulating and v regenerating bath. Hydrolysis of the cyanoethyl groups on -the cellulose during aging and processing procedures predominently carboxyethyl substituent groups on the cellulose in place of the cyanoethyl groups in the final fiber product.

Reference to the average degree of substitution (D.S.) of the cyanoethyl cellulose as used herein includes products wherein the anhydroglucose units of the cellulose molecules have an average substitution from about 0.25 to about 0.65 of cyanoethyl groups or chemical groups derived from said cyanoethyl groups by hydrolysis or other chemical change which occurs during manufacture and aging of the material. Thus, the recitation of cyanoethyl cellulose is also meant to include cellulose having carboxyethyl groups and some carboxyamide substituent groups.

To obtain the average degree of substitution prescribed, the amount of acrylonitrile used will vary with the process and conditions employed for 1 the preparation of the regenerated cyanoethyl cellulose fibers. Preferably, the simultaneous cyanoethylation and xanthation procedure uses from about 20 to about 50 percent acrylonitrile based on the weight of the cellulose. Other methods require higher proportions of acrylonitrile to obtain the prescribed degree of substitution.

The composition of the viscose of this invention, except for the amount of acrylonitrile as described above, is not particularly critical. For example, viscose compositions containing cellulose ranging from about 3 to about 12 wt. percent, caustic from about 3 to about 12 wt. percent, and carbon disulfide from about 20 to about 60 percent based on the weight of the cellulose, are useful. Conventional viscose additives can be incorporated if desired. The cellulose can have a wide molecular weight range and the viscose will have a salt test and ball-fall viscosity in the spinning range as is well-known.

The composition of the spinning bath tocoagulate the extruded viscose is also not critical and, for example, comprises about l to 15 wt. percent, sulfuric acid, about 1 to about 25 wt. percent sodium sulfate and 0 to 10 wt. percent zinc sulfate. Conventional spinning bath additives can also be incorporated in the bath if desired.

After spinning, the wet-gel acidic fibers are preferably run directly through a heated, dilute acid bath having a high salt concentration. This bath continues regeneration of the fibers while limiting any swelling thereof. The fibers, if desired, may be stretched to any degree to just below their breaking point in this regeneration bath.

After this, the fibers are run through an alkaline bath also having a high salt content and preferably containing a lubricant for cellulosic fibers. This bath neutralizes the acidic fiber while limiting swelling thereof and deposits a small amount of lubricant thereon. From about 0.5 to about 5 percent and preferably from about 1 to 2 wt. percent of lubricant is incorporated in the the proportions mentioned above may be incorporated in a concentrated aqueous salt solution through which the fibers are passed after leaving the neutralizingbath. As a further alternative, the lubricant for the cellulosic fiber can be applied from a non-swelling organic carrier or solvent for the lubricant such that enough lubricant is deposited on the individual fibers to substantially decrease inter-fiber cementation. The carrier or solvent will be removed when the fiber is dried.

As a still further alternative, the lubricant, if liquid, can be applied to the cellulosic fiber alone without water or organic carrier or solvent. For example, the wet fiber, after leaving the neutralizing bath,-before or after squeezing to remove some water, can be passed through a mist of atomized lubricant to also deposit a sufficient amount to substantially decrease inter-fiber cementation when the fibers are dried. The amount of lubricant depositedon the fibers by these alternative methods should be equivalent to the amount deposited when a lubricant is incorporated in the salt bath since higher amounts will reduce the self-bondable property of the fibers.

.The neutralized lubricated gel fibers if not so treated previously are pressed, centrifuged or otherwise treated to remove excess water. The dewatered fibers may be cut into staple length, if desired, and then dried to normal moisture regain content or lower moisture content by air drying or heating to temperatures up to or slightly above the boiling point of the salt solution.

These fibers are then usually dry blended with other fibers including rayon, cotton, flax, wool, synthetic thermoplastic fibers, glass, and the like and the mass of fibers is carded to form a batt of a uniform mixture of fibers. This batt is wet out or steamed to activate the self-bonding regenerated cyanoethyl cellulose fibers and then the batt is pressed and dried to form a nonwoven fabric having good dry strength. Wet strength of the non-woven can be improved by incorporating a wet-strength agent e.g., an epichlorohydrin modified polyamide, in the water or aqueous mediumused to activate the self-bonding fibers, and effecting a cure of the wet-strength resin after drying.

The salts used to prevent or limit the swelling of the freshly spun fibers are those disclosed in US. Pat. No. 3,419,345 of Dec. 31, 1968, to E. G. Parrish which prevent or limit the swelling of freshly formed regenerated cellulosic fibers. This patent is incorporated herein by reference. It concerns a method for neutralizing acidic or alkaline structures of freshly formed highly swellable hydrophilic gel fibers of a cellulose derivative to produce a soft pliable, highly absorbent product. Neutralization is accomplished by intimately contacting the freshly formed unswollen fiber with an aqueous concentrated buffered salt solution. The patent claims (1) a process for neutralizing a highly swellable hydrophilic gel fiber of a cellulose derivative which comprises intimately contacting the freshly formed unswollen fiber with an aqueous, concentrated buffered salt solution, the said saltsolution having a pH in the range of from about 5.0 to about 9.0.

The buffering salts given as examples in said patentare potassium acid phthalate dipotassium phthalate (pH 5.0 6.2), sodium dihydrogen phosphate disodium hydrogen phosphate (pH 5.9 8.0), boric acid Borax (pl-l 6.8 9.0), disodium hydrogen phosphate critic acid (pH 5 8), critic acid sodium citrate, I

and sodium bicarbonate Na,CO The salts given as examples in said patent to prevent or limit swelling of the fibers are those having multivalent and univalent cations but preferably magnesium, ammonium and sodium as well as other alkali metals. The anions of these salts are preferably the .not be limited on the alkaline side to a pH of 9 since the process can be carried out satisfactorily at a pH of l 1 but preferably less than a pH of 12.

Lubricants for cellulosic fibers which are incorporated into the concentrated buffered salt solutions or other salt solutions for application to the fibers must be compatible with these salt solutions so that the lubricant will not precipitate or the salt will not precipitate from the solution.

The lubricants for cellulosic fibers which are compatible with the salt solutions used herein are wellknown to those skilled in the art and include, for example, alkali and alkaline earth metal alkyl sulfates wherein the alkyl groups range from about 10 to about 18 carbon atoms, e.g., sodium lauryl sulfate; alkali and n alkaline earth metal salts of a sulfated 3 to 15 moleethoxylated primary fatty alcohol having 10 to 18 carbon atomsand mixtures thereof, e.g., a 3 mole ethoxylated sodium lauryl sulfate; alkali and alkaline earth metal alkyl phosphates wherein the alkyl groups range from about six to about 12 carbon atoms e.g., dipotassium hexyl phosphate; alkyl pyridinium chlorides wherein the alkyl groups have from six to 18 carbon atoms, e.g., lauryl pyridinium chloride; cationic quaternary ammonium compounds having the general formula:

n, R, ll l wherein R is an aliphatic hydrocarbon radical containing 12 to 18 carbon atoms, R and R are short chain alkyl, alkylol or aliphatic radicals which together with the nitrogen (N) atom form a heterocyclic ring, R, is a short chain alkyl or lower araklyhand A is an anion from the group including. halides, sulfates, alkyl sulfates, nitrates, phosphates, acetates, citrates and the like. These compounds are disclosed, for example, in

US. Pat. No. 2,668,785 of Feb. 9, 1954. Typical com N-ethyl the bonding strength of the regenerated cyanoethyl cellulose fibers when used as binder fiber in a dry laid nonwoven fabric. Examples of other lubricants for cellulosic fibers which may or may not be compatible with the salt solutions include di(C,C )alkyl cyclohexylamine salts of C C, fatty acid esters of hexitans, e.g., sorbitan monooleate; C C fatty acid esters of polyethylene glycols; C C fatty acid esters of pentaerythritol, and the like.

While the wet fibers must be dried down to a water content which will permit them to be carded, it is preferred that they are dried to the normal moisture regain of the regenerated cyanoethyl cellulose fibers which is that moisture content which the fibers will reach after being dried to about zero percent moisture content and then allowed to stand at ambient temperature and humidity for a time sufficient for the water content of the fiber to reach an equilibrium state with said ambient humidity. Moisture regain for the fibers of this invention will ordinarily range from about 8 to 16 percent moisture. Under plant conditions, the moisture content of the dry yarn will be from about 1 l to 14 percent.

The term self-bendable as applied herein to the regenerated cyanoethyl cellulose fibers is meant to define fibers which of themselves and without the addition of adhesive material, either alone or when blended with other non-self-bondable fibers, the fibers wet with water and then dried, will provide a durable non-woven fabric product.

The fibers of this invention and non-wovens prepared therefrom, and methods of their manufacture are demonstrated in the following examples.

EXAMPLE I Regenerated cyanoethyl cellulose fibers having an average D.S. of about 0.38 were prepared as follows: Amounts of 8.25 lbs. of carbon disulfide and 10.75 lbs. acrylonitrile (34 and 45 percent respectively, based on the weight of the cellulose in the viscose to be prepared) were premixed in a five gallon safety can and the mixture charged to an evacuated churn by gravity through a valved stainless steel line. The churn contained a 77 lb. batch of alkali cellulose crumbs and was kept at a temperature during a two hour reaction (churning) time of 15 to 32C. Sufficient water and caustic were added to the churn after the two hour reaction to produce a viscose of 8.0 percent cellulose and 6.0 percent sodium hydroxide (caustic) based on the weight of the viscose, and 34 percent carbon disulfide and 45 percent acrylonitrile based on the weight of the cellulose, after mixing in the churn for an additional one and three quarter hours.

This viscose, having a common salt test of l72l and a ball-fall of 40-50 seconds, was then pumped to a spinning machine where it was passed through a filter and extruded through a 5,000 hole spinneret into an aqueous coagulating and regenerating bath consisting of 10.5 percent sulfuric acid, l percent zinc sulfate and 17 percent sodium sulfate and having a temperature of 50C. The fibers were immersed in this bath for a distance of 24 inches. They were then run around a first godet, through a second aqueous bath consisting of 0.5 percent sulfuric acid, 0.5 percent zinc sulfate and 17 percent sodium sulfate maintained at a temperature of 90C. and then around a second godet. The fibers were stretched between the godets 50 percent. They were then run through an aqueous alkalizing bath consisting of 2 percent of a finish for cellulosic fiber consisting of the sodium salts of a sulfated 3 mole ethoxylated mixture of primary fatty alcohols having from 12 to 15 carbon atoms, 2 percent sodium carbonate and 17 percent sodium sulfate at a bath temperature of about 45C. and a pH of about 10.

The neutralized, unswollen fibers were then squeezed between rollers to remove some of the water, cut to 1 inch lengths and dried by heating at C. to a moisture content of less than 12 percent by weight.

These soft dried fibers were machine cardable without mixing with other fibers. They were blended with non-derivatized viscose rayon staple fiber of about the same length and denier at a ratio of parts rayon fibers to 20 parts of cyanoethyl cellulose fibers. The blend was double carded into batts and the batts were wet out with water containing 0.2 percent by weight of epichlorohydrin modified polyamide wet strength agent. The batts were drained, dried and cured at 300F. for 3 minutes under a pressure of psi.

The non-woven batts had very good wet and dry strength, good softness and good drape characteristics.

EXAMPLE II Regenerated cyanoethyl cellulose fibers were prepared as described in Example I to the point of coagulation and regeneration thereof in the acid spinning bath. The fibers had a filament denier of 3. The acidic fibers were collected and 4.5 grams thereof were cut to 1 inch lengths. The cut fibers were placed in 4,500 mls. of an aqueous solution containing 0.015 weight percent sodium lauryl sulfate and stirred for 2 minutes. This slurry was then poured into a Noble and Woods mold 12 X 12 inches) containing 6.750 liters of water. This slurry was stirred briefly to distribute to fibers and then a sheet was cast. The sheet was then dried on a Noble and Wood hot plate at 233F. (1 12C.). The resulting sheet was very horny, strongly bonded and could not be carded.

The foregoing example demonstrates the difficulty in obtaining a cardable fiber in accordance with the procedure of Example VII of U.S. Pat. No. 3,525,735.

EXAMPLE Ill TABLE I Dried Fiber Condition Boardy, not cardable Treatment Bath l) 100% water 2) 2% laurylpyridinium chloride 3) 2% Sodium carbonate 2% finish of Example 1* 4) 2% Sodium carbonate 2% laurylpyridinium chloride 5) 2% Sodium carbonate 17% sodium sulfate Harsh, not cardable Sodium salts of a sulfated 3 mole ethoxylated mixture of primary fatty alcohols having l2 to 15 carbon atoms.

The above table demonstrates various other treatments of the regenerated cyanoethyl cellulose fibers prior to drying. None of these approaches were successful in preparing soft, cardable fibers.

EXAMPLE IV Regenerated cyanoethyl cellulose fibers were prepared as described in Example 1 to the point of stretching the filaments in a hot bath. The stretched filaments were then run through a neutralizing bath similar to Example 1 except that different lubricants were employed. The fibers were then processed and dried as in Example I. The following table shows the result of this work.

TABLE I1 Amount in Dry fiber Lubricant bath, properties I N-cetyl, N-ethyl morpholinium ethosulfate 1.2 Soft, cardable 50 2) Dipotassium hexyl phosphate l.2 2.0 3) Sodium lauryl sulfate 1.2 2.0 4) Lauryl pyridinium chloride l.2

The above finishes for cellulosic fibers are presented in their order of degree of softness although each lubricant is capable of producing a soft fiber. Furthermore, as the amount of lubricant used is increased over about 2 percent, a decrease in non-woven strength is noted.

Various changes and modifications may be made practicing this invention without departing from the spirit and scope thereof and therefore the invention is not to be limited except as defined in the claims.

We claim:

1. Dry, soft, cardable, self-bendable fibers of regenerated cyanoethyl cellulose wherein the average degree of substitution ranges from about 0.25 to about 0.65, said dry fibers having been prepared by neutralizing the unswollen acidic gel fibers of regenerated cyanoethyl cellulose with an aqueous concentrated buffered salt solution and bringing the wet fibers in intimate contact with a lubricant for cellulosic fibers under non-swelling conditions, and then drying the fibers to a water content which is their normal moisture regain.

2. The dry, cardable fibers of claim 1 wherein the lubricant has been incorporated in said aqueous concentrated buffered salt solution at a concentration of from about 0.5 to about 5 percent based on the weight of the solution.

3. The dry, cardable fibers of claim 1 wherein the buffered salt solution is a solution of sodium carbonate as the buffering agent and sodium sulfate as the concentrated salt.

4. The dry, cardable fibers of claim 1 wherein the lubricant is from the group including alkali and alkaline earth metal salts of a sulfated 3 to mole ethoxylated primary fatty alcohol having 10 to 18 carbon atoms, alkali and alkaline earth metal alkyl phosphates wherein the alkyl group has from six to 12 carbon atoms, alkyl pyridinium chlorides wherein the alk yl group has from six to 18 carbon atoms, and cationic quaternary ammonium compounds having the general formula wherein R is an aliphatic hydrocarbon radical containing 12 to 18 carbon atoms, R and R are short chain alkyl, alkylol or aliphatic radicals which together with the nitrogen (N) atom form a heterocyclic ring, R is a short chain alkyl or lower aralkyl group and A is an anion from the group including halides, sulfates, alkyl sulfates, nitrates, phosphates, acetates and citrates.

5. The dry, cardable fibers of claim 4 wherein the lubricant has been incorporated in said aqueous concentrated buffered salt solution and said solution contains sodium carbonate as the buffering agent and sodium sulfate as the concentrated salt.

6. The dry, cardable fiber of claim 5 wherein the lubricant is the sodium salt of a sulfated 3 mole ethoxylated mixture of primary fatty alcohols having from 12 to 15 carbon atoms.

7. The dry, cardable fiber of claim 5 wherein the lubricant is N-cetyl, N-ethyl morpholinium ethosulfate.

8. A durable, dry-laid non-woven fabric containing as the binder fibers at least about 5 percent by weight of regenerated cyanoethyl cellulose having an average degree of substitution of about 0.25 to about 0.65, said binder fibers having been prepared by neutralizing the unswollen acidic gel fibers of regenerated cyanoethyl cellulose with an aqueous concentrated buffered salt solution and bringing the wet fibers in intimate contact with a lubricant for cellulosic fibers under non-swelling conditions, and then drying the fibers to a water content which is their normal moisture regain.

9. The durable, dry-laid non-woven fabric of claim 8 wherein the lubricant has been incorporated in said aqueous concentrated buffered salt solution at a concentration of from about 0.5 to about 5 percent based on the weight of the solution.

10. The durable, dry-laid non-woven fabric of claim 9 wherein the lubricant is from the group including alkali and alkaline earth metal salts of a sulfated 3 to 15 mole ethoxylated primary fatty alcohol having 10 to 18 carbon atoms, alkali and alkaline earth metal alkyl phosphates wherein the alkyl group has from six to 12 carbon atoms, alkyl pyridinium chlorides wherein the alkyl group has from six to 18 carbon atoms, and cationic quaternary ammonium compounds having the general formula wherein R is an aliphatic hydrocarbon radical containing 12 to 18 carbon atoms, R and R are short chain alkyl, alkylol or aliphatic radicals which together with the nitrogen (N) atom form a heterocyclic ring, R, is a short chain alkyl or lower aralkyl group and A is an anion from the group including halides, sulfates, alkyl sulfates, nitrates, phosphates, acetates and citrates. 

2. The dry, cardable fibers of claim 1 wherein the lubricant has been incorporated in said aqueous concentrated buffered salt solution at a concentration of from about 0.5 to about 5 percent based on the weight of the solution.
 3. The dry, cardable fibers of claim 1 wherein the buffered salt solution is a solution of sodium carbonate as the buffering agent and sodium sulfate as the concentrated salt.
 4. The dry, cardable fibers of claim 1 wherein the lubricant is from the group including alkali and alkaline earth metal salts of a sulfated 3 to 15 mole ethoxylated primary fatty alcohol having 10 to 18 carbon atoms, alkali and alkaline earth metal alkyl phosphates wherein the alkyl group has from six to 12 carbon atoms, alkyl pyridinium chlorides wherein the alkyl group has from six to 18 carbon atoms, and cationic quaternary ammonium compounds having the general formula
 5. The dry, cardable fibers of claim 4 wherein the lubricant has been incorporated in said aqueous concentrated buffered salt solution and said solution contains sodium carbonate as the buffering agent and sodium sulfate as the concentrated salt.
 6. The dry, cardable fiber of claim 5 wherein the lubricant is the sodium salt of a sulfated 3 mole ethoxylated mixture of primary fatty alcohols having from 12 to 15 carbon atoms.
 7. The dry, cardable fiber of claim 5 wherein the lubricant is N-cetyl, N-ethyl morpholinium ethosulfate.
 8. A durable, dry-laid non-woven fabric containing as the binder fibers at least about 5 percent by weight of regenerated cyanoethyl cellulose having an average degree of substitution of about 0.25 to about 0.65, said binder fibers having been prepared by neutralizing the unswollen acidic gel fibers of regenerated cyanoethyl cellulose with an aqueous concentrated buffered salt solution and bringing the wet fibers in intimate contact with a lubricant for cellulosic fibers under non-swelling conditions, and then drying the fibers to a water content which is their normal moisture regain.
 9. The durable, dry-laid non-woven fabric of claim 8 wherein the lubricant has been incorporated in said aqueous concentrated buffered salt solution at a concentration of from about 0.5 to about 5 percent based on the weight of the solution.
 10. The durable, dry-laid non-woven fabric of claim 9 wherein the lubricant is from the group including alkali and alkaline earth metal salts of a sulfated 3 to 15 mole ethoxylated primary fatty alcohol having 10 to 18 carbon atoms, alkali and alkaline earth metal alkyl phosphates wherein the alkyl group has from six to 12 carbon atoms, alkyl pyridinium chlorides wherein the alkyl group has from six to 18 carbon atoms, and cationic quaternary ammonium compounds having the general formula 